0.8 Hours -
The FL-708 spacers needed a final touch before they were ready for the flaps, so I ventured into the garage for a quick work session after returning home from my real work. All that needed to be done was to drill a single hole in each spacer so that they can be clecoed to the inboard and outboard flap ribs. The second hole in the spacer is drilled using the skin/rib as a guide. After measuring for the location of the holes, center punching them, and finally drilling, I should have stopped for the day, but I pressed on (keep reading to see why I should have quit at this point).
I finished the FL-708 spacers by drilling one #40 hole in each spacer. The other hole will be drilled using the skin/rib as a guide. The top spacer is drilled while the bottom spacer has only been center punched.
Next, I located the appropriate ribs for the left flap and drilled them to the spar. The internal ribs are pre-punched with small holes, which momentarily confused me since the plans say that they need to be riveted to the spar with LP4-3 rivets. So far, if the hole needs to be final drilled to #30 or larger, Van’s has generally pre-punched it with the larger hole size. I scanned the plans a bit more before deciding that enlarging the holes to #30 was appropriate.
Once the skeleton was assembled, I clecoed on the bottom skin. Flap construction is a bit different from the other control surfaces because the rear spar is built into the bottom skin as a bend. The flaps take on a lot of force when they are extended, so I’m guessing using only ribs wouldn’t be strong enough and using a traditional rear spar would make the trailing edge to wide.
The left flap skeleton and bottom skin temporarily clecoed together.
The instructions are very clear that aft end of the interior flap ribs need to touch the bottom skin rear spar, but some of them won’t and will require shims to be made. I inspected my assembly and found that the gap between the rib and spar ranged from none to fairly sizeable. I decided that three of the ribs would require shims, and .025 aluminum would be sufficient for all of them.
Here's a composite of the aft ends of the four interior ribs on the left flap. They range from no gap, to a big gap with the shim already in place. I decided to shim all except for the one on the left.
I cut enough shims so that I would have them for the right flap as well. After sliding the shims into place, it was clear that they would fill the gaps, so I started drilling the ribs/shims to the rear spar. The aft end of the ribs are not pre-punched, so the hole in the rear spar is used as a guide for drilling both the shim and the rib. Once again, Van’s pre-punched the rear spar with a small hole that needed to be enlarged to #30.
Drilling the rear spar is where my problems arose and my work session ended. The first rib was easy since it didn’t require a shim. However, on the second one, the drill bit grabbed the shim and started spinning it. Not thinking, I had my finger in the way and the spinning shim was, essentially, a spinning blade that cut into my finger on two of its rotations. On first inspection, the cuts didn’t appear to be too bad, so I altered my technique and moved on to the next rib. About halfway through drilling, I felt something warm on my hand…blood was pouring out of my finger, down my hand, and on to the work bench. Being a dedicated aircraft builder, I wrapped my finger in a paper towel (heavy-duty shop paper towel of course), applied some duct tape, and continued working until all the ribs/shims were drilled. I then went inside to inspect the damage. The amount of blood was deceptive as the cuts weren’t too bad.
After bandaging my wounds, I briefly returned to the garage to inspect the shims. They are ok, but I may redo them and make them slightly larger. At least the second time around I will know to keep my fingers out-of-the-way!
